In U.S. Internet searches, Google sites dropped a bit while the Yahoo and Microsoft Web sites experienced an increase in visitors in April 2010, according to the latest comScore Core Search Report. The research company also reports there were 15.5 billion searches last month.

“Both Yahoo! Sites and Microsoft Sites have experienced gains due in part to the introduction of new site navigation experiences that tie content and related search results together within several channels,” according to the comscore press release.

“These features provide search results to users as they navigate through topical content and meet comScore’s established criteria for counting search queries,” added comScore. “Ask Network captured 3.7 percent of the search market, followed by AOL LLC with 2.4 percent.”

The ranking in terms of searches:

Google – 10 billion

Yahoo – 2.8 billion

Microsoft – 1.8 billion

Ask Network – 574 million

AOL LLC – 371 million

The comScore disclaimer: “Based on the five major search engines including partner searches and cross-channel searches. Searches for mapping, local directory, and user-generated video sites that are not on the core domain of the five search engines are not included in the core search numbers.”